Most of the eDirectBuy orders come back, "Out of Stock" then you get lots of spam from then on... I do not know anybody who has placed a successful order.
The lowest I have seen is $64 for Academic XP Home, $85 for Windows XP Home, and $ 105 to $129 for Windows XP Professional...
Any thing otherwise is suspect, because they can always sell them for the above on eBay... so why would they sell to you.
Also, "Unlimited Installs" is a red flag.
You won't get your money back, either.